The CHCl3 levels in the NIEHS drinking water were determined for a 9 month period. These levels were found to inversely correlate with apparent reproductive failures in certain experimental animals in the institute. A sampling of the total organics revealed the presence of 51 different partially halogenated hydrocarbons ranging from C1-C5. Chemical oxygen demand determinations for the months of March and August (considerably different CHCl3 levels found) indicate that there is little difference in total organics concentration. These findings suggest that higher concentrations of the larger organic molecules found in tap water during the colder months due to less extensive degradation on chlorination could be a minor acute toxicity problem in regard to reproduction.